Added repr string for Grouper and TimeGrouper

Author: tp

doc/source/whatsnew/v0.21.1.txt

@@ -22,7 +22,7 @@ Other Enhancements
 ^^^^^^^^^^^^^^^^^^
 
 - :meth:`Timestamp.timestamp` is now available in Python 2.7. (:issue:`17329`)
--
+- :class:`Grouper` and :class:`TimeGrouper` now have a friendly repr output (:issue:`18203`).
 -
 
 .. _whatsnew_0211.deprecations:

pandas/core/groupby.py

@@ -206,12 +206,13 @@ class Grouper(object):
     sort : boolean, default to False
         whether to sort the resulting labels
 
-    additional kwargs to control time-like groupers (when freq is passed)
+    additional kwargs to control time-like groupers (when ``freq`` is passed)
 
-    closed : closed end of interval; left or right
-    label : interval boundary to use for labeling; left or right
+    closed : closed end of interval; 'left' or 'right'
+    label : interval boundary to use for labeling; 'left' or 'right'
     convention : {'start', 'end', 'e', 's'}
         If grouper is PeriodIndex
+    base, loffset
 
     Returns
     -------
@@ -233,6 +234,7 @@ class Grouper(object):
 
     >>> df.groupby(Grouper(level='date', freq='60s', axis=1))
     """
+    _attributes = ('key', 'level', 'freq', 'axis', 'sort')
 
     def __new__(cls, *args, **kwargs):
         if kwargs.get('freq') is not None:
@@ -333,6 +335,14 @@ def _set_grouper(self, obj, sort=False):
     def groups(self):
         return self.grouper.groups
 
+    def __repr__(self):
+        attrs_list = ["{}={!r}".format(attr_name, getattr(self, attr_name))
+                      for attr_name in self._attributes
+                      if getattr(self, attr_name) is not None]
+        attrs = ", ".join(attrs_list)
+        cls_name = self.__class__.__name__
+        return "{}({})".format(cls_name, attrs)
+
 
 class GroupByPlot(PandasObject):
     """

pandas/core/resample.py

@@ -1025,7 +1025,10 @@ class TimeGrouper(Grouper):
     Use begin, end, nperiods to generate intervals that cannot be derived
     directly from the associated object
     """
-
+    _attributes = Grouper._attributes + ('closed', 'label', 'how',
+                                         'nperiods', 'fill_method', 'limit',
+                                         'loffset', 'kind', 'convention',
+                                         'base')
     def __init__(self, freq='Min', closed=None, label=None, how='mean',
                  nperiods=None, axis=0,
                  fill_method=None, limit=None, loffset=None, kind=None,

pandas/tests/test_resample.py

@@ -3400,3 +3400,10 @@ def test_aggregate_with_nat(self):
 
             # if NaT is included, 'var', 'std', 'mean', 'first','last'
             # and 'nth' doesn't work yet
+
+    def test_repr(self):
+        result = repr(TimeGrouper(key='A', freq='H'))
+        expected = ("TimeGrouper(key='A', freq=<Hour>, axis=0, sort=True, "
+                    "closed='left', label='left', how='mean', "
+                    "convention='e', base=0)")
+        assert result == expected